Vaccine for the H1N1 influenza pandemic will be distributed on a three-day turnaround time from four regional warehouses around the country next month. The vaccine deliveries, expected to equal 20 million doses a week by the end of October, will be distributed among 90,000 immunization “providers,” including health departments, hospitals, clinics, doctors’ offices and pharmacies.

Those were among the details unveiled Friday by the Centers for Disease Control and Prevention as part of the federal government’s increasingly complex response to the pandemic of H1N1 influenza, also known as swine flu.

“This is a huge logistical process. There’s not [going to be] a sudden appearance of vaccine in 90,000 refrigerators around the country,” said Jay Butler, an epidemiologist who leads the CDC’s task force on the vaccine.

About 3.4 million doses of nasal-spray flu vaccine — which can be used only by people age 2 to 49 — are expected to be available the first week of October. The form of the vaccine that can be injected, which will form the vast bulk of the 195 million doses the government has ordered, won’t be available until later in October when many experts think the flu outbreak will be in full swing.